1. Statement of the Technical Field
The inventive arrangements concern hybrid couplers, and more particularly hybrid couplers having a miniaturized design and capable of producing from a single input signal, two output signals that are 180° out of phase.
2. Description of the Related Art
Hybrid couplers are passive devices used in the field of radio frequency (RF) systems. Typically such hybrid coupler devices can receive an input signal and produce two output signals where the input power is equally divided between two output ports. More particularly, 180° hybrid couplers are four-port devices that can receive an input signal and provide as an output two equally-split but 180 degree phase-shifted output signals. In RF systems, broadband 180° hybrids are frequently used for anti-phase power dividing and combining.
One problem with conventional 180° hybrid couplers is that they include multiple components such as Lange couplers that are a quarter wavelength in size, or in some implementations, transmission line structures that are a half wave length in size or larger. Open space is required around the periphery of such components to ensure their proper operation. These factors can result in a device which requires a large surface area on a circuit board or substrate. The use of high dielectric constant ceramic media and other techniques have been used to miniaturize these devices to some extent. However, for many applications, the overall size of these devices remains prohibitive, especially for lower operating frequencies. Below X-band, conventional coupler designs are generally too large for use in monolithic microwave integrated circuit (MMIC) designs. Ferrite versions of 180° hybrid couplers are also known, and can be made relatively small. However, the upper operating frequency of such devices is limited to about 3 GHz. Broadband ferrite versions of 180° hybrid couplers are also known to suffer from excessive loss at the high end of their operating band.